Test Point 33 - Leads K and L
TEST POINT 33 - Leads K and LThe diagnosis connection between the Digital Motor Electronics (DME) control unit and testers is established by means of the two leads K and L. If no diagnosis is possible, the following points must be checked:
Assignments:
7 - Lead L
8 - Lead K
10 - Ground
13 - Terminal 15
1. Continuity test (refer to wiring diagram)
Leads L: Pin 7 (19-pin diagnostic socket) - Pin 13 (DME plug)
Leads K: Pin 8 (19-pin diagnostic socket) - Pin 55 (DME plug)
2. Ground short test (refer to wiring diagram)
Leads L: The voltage at pin 7 (19-pin diagnostic socket) must be > 8 V when the ignition is on.
Lead K: The voltage at pin 8 (19-pin diagnostic socket) must be > 8 V when the ignition is on
Possible fault cause at < 8 Volt:
- Short to ground or open circuit in wiring or connectors.
- A defective control unit connected to the above leads. (May be any diagnosable control unit, need not necessarily be the DME control unit).
Checking: Disconnect plugs at diagnosable control units one after the other until the voltage is > 8 V. Replace responsible control unit.
- Tester faulty.
- No power supply at the diagnostic plug.
- No ground supply at diagnostic plug.
Notes on idling speed and idling CO testing:
a) Idling speed
Idle speed check value for engines at operating temperature:
840 ±40 rpm with manual transmission
880 ±40 rpm with Tiptronic
b) Idle speed CO of cars without catalytic converter
The CO level is adjusted at the idle potentiometer in the engine compartment. The following requirements must be observed:
- Engine at operating temperature
- Engine in good mechanical condition, ignition o.k.
- All loads switched off
- CO tester at operating temperature, calibrated and adjusted correctly
Adjusting value: 0.5 - 1.5 % CO
c) Idle speed CO of cars with catalytic converter
On these vehicles, adaptation of idle speed CO level takes place along with adaptation of the idle speed. As a result, only the actual condition can be checked on those vehicles. The following requirements must be observed when performing the checks:
- Engine at operating temperature
- Engine in good mechanical condition, ignition o.k.
- All loads disconnected
- Exhaust tester at operating temperature, calibrated and adjusted correctly
- Oxygen sensor plug connected Test value: 0.4 - 1.2 % CO
NOTE: After disconnecting the control unit plug or the battery, the engine must run at idle for at least 10 minutes before these values can be rechecked.
Coding the control unit
The DME control unit is coded using a jumper connection deviating from the control unit wiring loom. If the jumper connection is free, the control unit operates in controlled mode, i.e. with oxygen sensor regulation. If a 1k Ohm resistor is attached to the jumper, the control unit operates in uncontrolled mode, i.e. without oxygen sensor regulation.
The coding may also be read directly in the "Actual values" menu item using System Tester 9288.